1. Field of the Invention
This invention relates to a fuel-supply control system for an internal combustion engine or a gas-turbine engine, wherein a fuel-metering valve or valves are driven by an electric pulse train so as to open intermittently while the duty cycle of the pulse train is varied with an engine operating condition so that the amount of fuel supplied to the engine responds to the engine operating condition.
2. Description of the Prior Art
In a well-known fuel-supply control system for an internal combustion engine, a fuel-metering valve controls the amount of fuel injected into the engine combustion chamber through a fuel-injection valve. When the control valve opens, fuel flows therethrough to be injected via the injection valve. Since a pressure regulator controls the fuel pressure so as to keep the fuel flow rate constant when the control valve opens, the amount of fuel injected is proportional to the time during which the control valve is open. Generally, the control valve is of the electrically-driven type opening when energized, and is driven by an electric pulse train so as to open periodically. Thus, the amount of fuel injected per a unit time, or the time-averaged fuel injection rate, depends on the duty cycle of the pulse train corresponding to the open time rate of the control valve. Meanwhile the duty cycle of the pulse train is varied with an engine operating condition, such as an engine required power (a power required from the engine) or an engine load so that the amount of fuel injected per a unit time responds to the engine operating condition.
When the engine is operated under constant conditions, such a fuel-supply control system may produce therein relatively large fuel pressure pulsations. Each opening of the control valve causes a pressure pulsation, which travels back and forth within the system like a wave until completely damped. In the above constant conditions, the control valve usually opens periodically at a constant frequency for a constant period, so that the fuel pressure pulsations may interfere with each other to form relatively large fuel pressure pulsations. These resultant large pressure waves severely disturb the regulated pressure of the fuel injected, thereby lowering the stability or the accuracy of the control of the amount of fuel injected per a unit time.